Manic - I don't think that you can compare the two. There was only one Diana, and while she did a good job of what she did, she wasn't gunned down in active service.
These two policewomen aren't just people, they are representative of all serving police officers in the country (world, even) who were doing their job when they were shot. This affects many many more people, not just because of the loss of their lives but because of the "there but for the grace of God" feeling. Family members, friends, officers that are well known in the community - there are very few people in the country who wouldn't have some kind of attachment to a police officer, I would think.
I think it is perfectly reasonable for people to come and pay respects to them. And for their families to realise that people are truly shocked and saddened by what can happen to police officers doing their daily job. So no, it isn't mawkish in the same way that the whole Diana thing was.